Fix for newly discovered edge-case issue in clearfix CSS rule

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5237 2fea6a4d-a838-0410-917b-93a53c48e9d2
Use the HTML5 <main> tag

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5238 2fea6a4d-a838-0410-917b-93a53c48e9d2
'0' is a valid article title.


git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5239 2fea6a4d-a838-0410-917b-93a53c48e9d2
Merge remote-tracking branch 'upstream/master' into jquery-ui-integration